Display signs having surfaces which are in part formed by the light emitting ends of fiber optic cables have numerous indoor and outdoor applications. Some examples of these applications include outdoor highway signs, airport arrival/destination signs, and bus destination signs. By forming a part of the display surface of the sign with the light emitting ends of the fiber optic cables, the signs are visible at a greater distance than signs having surfaces which are not enhanced by fiber optic illumination.
An example of the use of fiber optic illumination of display signs is in the field of manually changeable message signs. In such signs, a plurality of fiber optic cables are bundled at one end and positioned in front of a light source. The other ends of the cables are arranged in a predetermined configuration on the display surface of the sign to provide the desired message. The drawback to such a display system is that the message provided by a single bundle of fibers is not changeable unless the ends of the fibers opposite the light source are physically reconfigured to produce another message.
Automatically changeable message signs using non-fiber optic elements are known in the art. An example of such a sign is disclosed in U.S. Pat. No. 3,916,403 to Mandzsu, et al., wherein magnetic indicator elements are magnetically flipped to produce a variety of messages. The technology referred to in the Mandzsu patent is commonly referred to as flip-dot technology in the art. The indicator elements are arranged in an array or matrix. By computer controlling the locations in the matrix at which indicator elements are magnetically flipped, a variety of messages may be produced. The indicating elements are typically painted a highly visible color to enhance sign visibility.
Thus, it is an object of the present invention to provide an automatically changeable message sign implementing flip-dot technology wherein light emitting end faces of fiber optic cables terminate at the surface of the indicator elements.
In any fiber optic system, however, the effective operation of the light transmitting fibers depends on an operational light source for illuminating the fibers. If the light source should fail, the fiber optic cables are rendered ineffective. Thus, it is desirable to provide a secondary light source in a fiber optic display system, to ensure continuous message display upon failure of the primary light source.
It is known to use a conventional prism beam splitter to split a light beam into two components, each of which can be used to illuminate a separate bundle of optical fibers. A pair of light sources may be located adjacent opposite surfaces of the prism so that each of the light sources can alternatively provide a source of light to both of the fiber optic bundles without changing position with respect to the prism. However, in such a system, a portion of the illumination provided by the light source is lost due to interference at the prism face. In addition, the illumination provided by the light source must be shared by two optical fiber bundles, reducing the illumination capacity of any one bundle.
Thus, it is another object of the invention to provide a fiber optic display system which provides primary and secondary light sources which alternatively shine light directly into bundled ends of fiber optic cables, the secondary light source automatically energizing upon failure of the primary source.